The part of the human eye responsible for focusing light onto the retina is the lens. The lens is a transparent, flexible structure that adjusts its shape to focus light rays properly, enabling clear vision at varying distances. When light enters the eye, it first passes through the cornea, then through the aqueous humor, before reaching the lens, which fine-tunes focus before the light hits the retina. The retina converts light into neural signals, which are transmitted to the brain via the optic nerve for visual interpretation.